Remove mysql use of DBDATA env var

This really isn't needed.  It's effective the same as the DSS_PATH env
var that is required by dbgen and qgen.  Just use DSS_PATH in its place.
Minor fixes in dbt3-run-workload

- Allow script to show usage before checking if required environment
  variables are set.
- Update execution of report script.
- Remove accidental addition of postgres specific commands.
Update user's guide

Remove sapdb documentation since the scripts probably don't work any
more, even though they are still in the repository.
Update report generation

Make better use of space on the index page.
List all charts on the test details pages.